There's probably some happy-ish medium of people toughing it out through a bad situation they don't feel they can change--and jumping at the first instance of itchy feet (which is admittedly harder at the moment).

Not sure when the job-hopping culture--especially on the west coast--really came in. I do associate it with post-dot com but I'd really have to look at the data. Certainly wasn't really true pre dot-com at large tech employers.